May, 1920J PHTSI0L0G1 251 



in mixtures of great complexity. The cleavage products are unstabli and highly reactive. 

 Many reactions take place giving a large Dumber of substances in varying amounts depending 

 on the concentration of BUgar, temperature, oxygen supply, etc. With ample wat< r supply 

 ami Oj the hexoses are burned a i thai there is no accumulation of end products. The rganic 

 acids found in succulents are the accumulating intermediate or end products of catabolism. 

 These organic acids break down easily in sunlight, i. c., split off CO». Joints of Opuntia 

 versicolor and 0. phaeacantha were the material used. The work consists largely of anal} 

 of these plants taken under a variety of external conditions and subjected to a number of 

 experimental conditions. Owing to the mucilaginous character of the material special 

 methods of analysis were necessary, and serious ermrs were found in existing method-; applied 

 to plant material. The material must lie quickly dried in order to destroy at once all enzyme 

 actions which by the usual methods of drying are greatly accelerated for some time by the 

 heat before the material is killed. One per cent HC1 for hydrolysis proved best. This com- 

 pletely hydrolyzes polysaccharides, its effect on cellulose is slight, much less than other 

 mineral acids. In making alcohol extractions it is exceedingly important that the plant acids 

 be neutralized with CaCOs, the addition of alkalies, e. g., NH 4 OH as commonly used, lead- 

 ing to molecular rearrangements. A study of various methods of determining pent ses 

 showed that these were open to serious sources of error and can be determined with accuracy 

 only after removal of hexoses by fermentation. A special method was devised for use with 

 alkaline copper solutions for all reducing sugars. Soxhlet's modification of Fehling's solu- 

 tion was used throughout. Reduction is carried out under precise conditions in a centrifuge 

 tube of special design graduated on neck and provided with glass stopper. After reduction 

 is completed, the tube is cooled and the solution made up to volume and thoroughly mixed. 

 The tube is then centrifuged, which results in the compact sedimentation of all CuO and for- 

 eign matter. The supernatant liquid is perfectly clear and the remaining Cu can be accu- 

 rately determined by means of the thiosulfate method according to Peters (Jour. Amer. Chem. 

 Soc. 34: 928-954; 422-454. 1912). Analyses embrace dry weight, total sugars, total poly- 

 saccharides, total hexose sugars, hexose polysaccharides, disaccharides, monosaccharides, 

 hexoses, total pentose sugars, pentosans, pentoses, cellulose, ash, and some micro-chemical 

 tests on starch formation and consumption. From these data conditions of equilibrium of 

 the various components are determined. Starch could not be determined by taka-distaase 

 because of the protective action of the mucilaginous substances. Rate of emission of CO2 

 was determined by absorption of C0 2 in standard Ba(OH) 2 solution and titrating unchanged 

 base with standard HC1 solution, using methyl orange. Joints 4 to 6 of cactus were hermet- 

 ically sealed in a light-proof desiccator provided with entrance and exit tubes, which was 

 immersed in a thermostat. C0 2 -free air was drawn through the apparatus by an electric 

 pump, pressure being regulated by a Palladin regulator for 4 to 12 hours and the stream of 

 air could be passed through a fresh tube without interrupting the experiment. Individual 

 plants show considerable variation in all components depending upon their location and 

 environmental conditions. The major portion of the carbohydrates is present as polysaccha- 

 rides, mainly as starch and a mucilaginous substance of pentosan nature. Results of analyses 

 of 0. versicolor and 0. phaeacantha gave fairly comparable results, with the total carbohydrate 

 content, and generally that of each constituent, higher in the last named species. — The fol- 

 lowing individual sugars were identified: 1-xylose, d-glucose, fruct so. saccharose, also glu- 

 curonic acid in small amount. The mucilaginous substances which play an important physi- 

 ological role were obtained by extraction with water filtered through fine silk repeatedly, and 

 precipitated with alcohol and dried. It was found by hydrolysis to contain 34.1 per cent 

 d-glucnse and 65.9 per cent 1-xylose, and a small amount of ash. It has an enormous water 

 holding power, though this does not prevent transpiration. The following seasonal varia- 

 tions in carbohydrate content were observed. Low water content and high temperature are 

 associated with: (1) increase of polysaccharides; (2) decrease 1 E m m saccharides; (3) 

 increase of pentosans. High water content and low temperature with: (I s ) decrease of poly- 

 saccharides; (2) increase of monosaccharides; (3) decrease of pent sans. The greatest 

 activity of the plant comes at the t ime when the content of mono- and disaccharides is highest, 

 and a supply of simple sugars above that required for the normal respiratory activity seems 



